Apple’s new iPod Nano, unveiled on Wednesday in San Francisco, weighs 1.5 ounces and is 0.27 inches thick. It comes in a 2GB version and a 4GB version, in black or white.

The Rokr, which will be available starting this weekend, can hold about 100 songs. It has a color display for viewing album art and features built-in dual-stereo speakers, as well as stereo headphones that also serve as a mobile headset with microphones.

iPod Nano accessories, including a dock, armband, lanyard/headphones and protective “tubes,” will be available next month.

Madonna appears via iChat to tout a new album, as well as the just-announced availability of her vast library on iTunes.

At the press event on Wednesday, Steve Jobs announces a partnership that will make the Harry Potter series of books available for audio download from the iTunes Music Store.